1. Field of the Invention
The embodiments of the invention generally relate to methods of connecting chips to chip carriers, ceramic packages, etc. (package substrates) and to a method that forms smaller than usual first solder balls and polymer pillars on the surface of a semiconductor chip and forms second solder balls on the corresponding surface of the package substrate to which the chip will be attached. The method heats the first solder balls and the second solder balls to join the first solder balls and the second solder balls into solder pillars.
2. Description of the Related Art
In conventional systems, solder balls are used to join chips to the package. However, it is becoming increasingly difficult to ensure solder ball reliability due to the following trends: smaller solder ball size (for higher I/O density); larger chip size; plastic packaging (with larger coefficient of thermal expansion (CTE) than ceramic packages); and the use of Pb-free solder (with higher reflow temperature and higher modulus than Pb-containing solder). The coefficient of thermal expansion mismatch between the chip and the package can result in high stress in the solder joints, which can cause cracks and eventually device failure.